More from WebMD

March 30, 2009 -- Babies who gain weight quickly in the first six months of life may be more likely to be obese by age 3, according to a new study.

"There is increasing evidence that rapid changes in weight during infancy increase children's risk of later obesity," says researcher Elsie Taveras, MD, PhD, of Harvard Medical School, in a news release. "The mounting evidence suggests that infancy may be a critical period during which to prevent childhood obesity and its related consequences."

In the study, published in Pediatrics, researchers compared weight-for-length measurements taken at birth, 6 months, and 3 years of age among 559 children.

Researchers say many previous studies on infant weight gain and childhood obesity focused mainly on body weight. But taking length into account as well as weight is a better indicator of body fat, similar to the body mass index (BMI) used to measure obesity in adults.

By the time the children reached age 3, 9% were obese.

The results showed the relationship between rapid weight gain for length between birth and 6 months and childhood obesity at age 3 was significant, even after adjusting for factors such as prematurity or babies who were underweight at birth.

Overall, children in the highest quartiles based on weight-for-length measurements at birth and 6 months had a 40% probability of childhood obesity by age 3, compared to 1% for children in the lowest quartiles.

"At first it may seem implausible that weight gain over just a few months early in infancy could have long-term health consequences, but it makes sense because so much of human development takes place during that period -- and even before birth," says researcher Matthew Gillman, MD, of Harvard's Obesity Prevention Program, in the news release. "Now we need to find out how to modify weight gain in infancy in ways that balance the needs of the brain and the body."